Aqueous solutions containing suspended colloids, present a problem with respect to removal of the colloidal particles. These colloids carry the same charges, and the electrostatic barrier repulsion prevents them from combining into larger colloid clusters for precipitation. Thus, some chemical and physical techniques are applied to help them precipitate. The phenomenon is known as coagulation where the colloids are combined with each other or flocculation where a flocculating agent is added.
A traditional method of coagulation is performed with the addition of an electrolyte. Charged particulates combine with the electrolyte ions neutralizing the charges. The neutral colloids combine to form larger colloid clusters, and finally precipitate.
A traditional method of flocculation is to use high-molecular-weight material to attract or trap the agglomerates with the flocculent, achieving a higher specific gravity and then settling down together. Starch and multiple charged ions are often used. Polymers with multiple charged sites are also commercially available for this purpose. In essence, various charged sites on these high-molecular-weight materials can collect colloids into an agglomeration or bridge format.
In traditional methods, dirty water is cleaned by treating with electrolytes such as Alum (Al2(SO4)3.12H2O), Ferric Chloride (FeCl3), Ferrous Sulfate, (FeSO4), Ferric Sulfate (Fe2SO4). The addition of those salts as an electrolyte may cause the pH to be lowered to the point where soluble ions (Al+3, Fe+3) are formed instead of hydroxide compounds. This is due to the Carbonic Acid formation and the sulfate ions (SO4−3). This practice in traditional methods produces unstable reactions creating turbidity and dispersion of the coagulation. In order to control dispersion it is usual to add either lime, Calcium Hydroxide (Ca(OH)2), Sodium Hydroxide (NaOH), Soda Ash (Na2CO3), or Sodium Bicarbonate (NaHCO3) or a combination thereof in order to balance the pH and the desired level of alkalinity. Traditional methods of treatment as described are only applications for colloidal removal from wastewater in a limited range of pH levels approaching 5 to about 7.
Determining the amount of electrolyte addition needed in order to obtain good coagulation results is as much an art as it is a science. Often, the correct formulation parameters is determined by experience coupled with trial and error testing with utilization of commercially available laboratory jar test equipment with jars of different shapes and or sizes. Formulation parameters of the present invention includes the amount of electrolyte, retention times, pH of solution and mixing characteristics.
The measurement of Zeta potential is another aid to determining the amount of electrolyte necessary to add to the aqueous solution being treated in order to coagulate or agglomerate its colloids into clusters. Equipment for measurement of Zeta potential is commercially available from Zeta-Meter, Inc, Staunton, Va. and its use is explained in their publication “Everything You Want to Know About Coagulations & Flocculation” Fourth Edition, 1993 (published by Zeta-Meter, Inc, available at www.mtec.org), and outlined below.
In order for colloids to combine together to form the colloid clusters, the repulsion between the colloids must be reduced. As explained in the Zeta-Meter Publication (Supra), Zeta potential is directly related to the charge strength on the colloids. Therefore, with Zeta potential instrumentation one can track the reduction of the charge force or barrier on the colloids. When the charge on the colloids is reduced sufficiently to allow the particles to collide, Van der Waals forces become the predominant force between the colloids and they form clusters. Because the Zeta potential is traditionally reduced to near zero, this mechanism is known as neutralization.
In traditional water treatment methods, those neutralized colloid clusters are removed from the aqueous solution.
Processes using addition of ballast flocculation and chemical precipitation are disclosed in U.S. Pat. No. 6,919,031. Numerous technologies have been developed over the years that are designed to maximize the efficiency and minimize the cost of each of the steps performed in a physical-chemical treatment process. Examples of such designs are disclosed in U.S. Pat. Nos. 4,388,195, 5,039,428, 5,730,864, 5,770,091, 6,210,587, and 6,277,285. Those technologies typically attempt to increase the coagulation and settling rates of suspended particles in the effluent. The coagulation and settling rates are influenced by a variety of factors, including the type and density of the particle and the concentration of solids being settled. However, the use of ballast material and inorganic compounds increase the solid volume, thus the resulting sedimentation is larger in volume, and the operation can become extremely complicated.
Another attempt to increase the flocculation is disclosed in U.S. Pat. No. 5,897,810 by using of shell fossil powder as a Ca2+ source, the method includes the use of aluminum sulfate to improve the floc forming mechanism, and gypsum as a flocculation agent. Perhaps the use of aluminum sulfate creates hazardous solids and the shell fossil powder requires rare and expensive material to be obtained.
The present invention uses some of the traditional electrolytes, but in a different way, in order to accomplish a unique series of process steps which increase the efficiency of the colloidal precipitation process and remove not only the colloids but also substantial amounts of specifically targeted dissolved solids. In particular, in the coagulation step, the colloid is not subjected to neutralization but rather carries a substantial charge thus achieving a Zeta potential specific to this process. This process subjects the colloid to substantially different than traditional reaction conditions.
With the present invention, there are two mechanisms that are responsible for bringing the targeted dissolved solids into becoming suspended solids and then progress into colloids. The first mechanism action engages when existing molecules with positive radicals or positive dipole charges bind with the trivalent negative ions PO4−3 thus binding the dissolved solids and bringing them to the colloidal state. The second mechanism supports the dissolved solids becoming suspended solids and colloids. That mechanism is the result of the ionic migration of Ca+2 ions as a dissolved solids (hardness) exchanging with the existing targeted dissolved solids.
In particular, the invention improves the colloid cluster charge availability and fragmentation process along with increasing the efficiency of a precipitation process. The present invention conditions the aqueous solution and its ionic, physical and chemical nature in three treatment steps and thereafter, if required, a separation process could be used to remove the resultant colloid clusters. In essence the process of the present invention conditions the aqueous solution in several steps to form flocculants, which can efficiently be removed by traditional separation processes, such as sedimentation and/or flotation.
The present invention has the objective, in the first step, to condition a stable colloidal suspension to become an unstable colloidal suspension (with a substantial charge or Zeta Potential) by way of ionic layer compression. The ionic compression enables the unstable colloidal suspension to agglomerate to form large colloidal clusters. The resulting colloidal clusters are kept in suspension e.g. by the aqueous solution being constantly mixed.
The present invention has the objective in the second step to further condition the large colloidal clusters so that they fragment into smaller clusters, which are kept in suspension e.g. by constant mixing of the aqueous solution.
In the third step of the present invention the fragmented colloid clusters are interacting with a flocculating agent (preferably a polymer type) that was injected into the aqueous solution. The flocculating agent flocculates the fragmented colloid clusters, which prepares the solution for a precipitation process (if desired) in the next step. The solution is normally constantly mixed in the third step in order to keep the flocculants in suspension and to permit uniform interaction of the flocculating agent and the suspension colloids. The flocculated solution could be delivered to a fourth step for separation and removal of the flocculates from the solution.
The present invention has the object to condition the aqueous solution so that the colloids can be clustered, sized, flocculated and then precipitated efficiently with the utilization of traditional separation means.